Conditions Necessary for Lateral Correlatability of Sequence Boundaries -An Overview

Mary Taiwo Olowokere and John Sunday Ojo
Federal University of Technology, Akure, Nigeria

The assumption that sequence boundaries have an eustatic origin, and hence a regional continuity, is a fundamental aspect of the conceptual framework and methodology of sequence stratigraphy as formulated by Exxon group. Given this fundamental assumption, it is not surprising to find that sequence boundaries are viewed by many authors as being regional on the scale of basin.

The- purpose of this study is to investigate whether the seismic-stratigraphic concept of regionally correlatable sequence boundaries is stratigraphically tenable when considered at the level of strata resolution achievable at outcrop. The paper focuses on the laterally extensive discrete surface of onlap, downlap and toplap and stratigraphic conditions necessary for their development.

The geometric properties and chronostratigraphic significance of sequence boundaries were formulated from seismic observations of strata relationships. These observations were however subject to the limitations of the vertical resolution of the seismic data. In this respect the conceptual framework was derived from a seismically simplified representation of the true stratal relationships.

The study showed that a surface of stratal discontinuity characterized by on lap, downlap or toplap can only be discrete and correlatable over an extremely limited area, except under specific and restricted conditions. Therefore, sequence boundaries defined from onlaps, down lap or toplap should not be expected to be correlatable as discrete and valid stratigraphic surfaces over large distances in any study area.